1. Field of the Invention
This invention relates to a method of preparing drawing data for a vector-scan type charged beam exposure system which draws patterns of a semiconductor integrated circuit or the like on a mask or a semiconductor wafer.
2. Description of the Related Art
A conventional method of preparing charged beam drawing data will be described below with reference to a flow chart shown in FIG. 8. Pattern data output from a CAD (computer aided design) system is first stored in a data base 1. Ordinarily, this pattern data has a multiple hierarchic structure constituted by data representing groups which include some figures (cells) and placement information for the cells. The pattern data stored in the data base 1 are flattened into figure processing data without a hierarchic structure in a hierarchic structure flattening step 2 and are stored in a data base 3. At this time, all data are expressed as fundamental figures such as rectangles, trapezoids and other polygons. In some cases, reiterating disposition information may be attached to the data on each fundamental figure.
In a field division step 4, the figure processing data stored in the data base 3 are divided with respect to each unit size of drawing region (hereinafter referred to as "field") which depends on a charged beam exposure system and are thereafter stored in a data base 5. Next, various figure modification processings are performed in an overlap-removal/tone-reversal step 6 and a figure magnification/reduction processing step 8. That is, in the overlap-removal/tone-reversal step 6, overlaps between the fundamental figures are removed and, at the same time, the data undergo tone-reversal if necessary and are stored in a data base 7. At this time, the figures which have reiterating disposition information are all exploded. Then, in figure magnification/reduction processing step 8, the figure processing data stored in the data base 7 undergoe magnification or reduction of each fundamental figure, and are thereafter stored in a data base 9. In this step, magnification or reduction of each fundamental figure is effected to an extent corresponding to a degree of necessary fine adjustment for a specific manufacturing technique, such as etching in order that the patterns can be actually formed by this technique in conformity with the design. The magnifying or reducing operation is performed in consideration of connections between fundamental figures.
After having undergone the processing modifying the figures, the figure processing data is finally processed in a formatting step 10 in such a manner that polygons in the fundamental figures are divided into rectangles or trapezoids and are converted into a format suitable for the charged beam exposure system, finally being stored as drawing data for changed beam exposure system in a data base 11.
In the conventional method of preparing charged beam drawing data, pattern data of a multiple hierarchic structure output from a CAD system are flattened into data on fundamental figures. Moreover, figures with reiterating disposition information are all exploded, and the data thereafter undergoes figure modification processing including overlap-removal/tone-reversal processing and figure magnification/reduction processing, thereby necessitating a large data storage capacity for preparation of charged beam drawing data as well as requiring much time for processing.
Under the existing conditions of increasingly developed design for high-density semiconductor devices, the data storage capacity needed for preparation of drawing data has become excessive, and it is possible that, in practice, necessary charged beam drawing data cannot be prepared.